The present invention relates to the use of certain aminocrotonates as hardeners for epoxide resins.
Synthetic resins based on epoxide resins are distinguished by numerous positive properties, e.g. good adherence to organic and inorganic substrates, good solvent resistance and high chemical resistance. Due to their chemical structure, however, epoxide resins which have been hardened with amines are often brittle, with glass transition ranges above 20.degree. C. This applies particularly to those epoxide resins which are based on 2,2-bis(4-hydroxyphenol)propane (bisphenol A) and epichlorohydrin. These synthetic resins therefore fail to meet the practical requirements in all fields of application for which a certain degree of flexibility is required. This applies particularly to the building industry, where permanent bridging of shrinkage cracks, e.g. in concrete, is required.
Internal increase in flexibility can be achieved to a certain extent by a reduction in the crosslink density while an external increase in flexibility may be achieved by the addition of plasticizer. External flexibilizing agents such as tar, phthalic acid esters, high boiling alcohols or vinyl polymers are not reactive and do not become incorporated in the polymer network.
An internal increase in flexibility by reduction of the crosslink density may be achieved by reducing the functionality of the hardener. The long chain, low functional amino amides based on dimerized fatty acids which have been widely and successfully used for a long time for this purpose are, however, not suitable in all fields.
Good and permanent increase in flexibility of the epoxide resins may be obtained by a combination with polyurethanes. Thus, for example, elasticized synthetic resins of epoxide resins, polyfunctional carbamic acid aryl esters and polyamines have been described in German Offenlegungsschrift 1,252,606. Synthetic resins prepared by these means have, however, two significant disadvantages. First, the use of a three component system is not always simple. Secondly, phenols or substituted phenols are released in the course of hardening of such synthetic resins since they are not chemically bound and in the long term they migrate from the synthetic resins, with the result that the properties of the product suffer.
German Auslegeschrift 2,418,041 describes a process for the preparation of elasticized molded parts and sheet products, in which certain epoxide compounds are reacted with amine compounds which have been obtained by the hydrolysis of certain prepolymeric ketimines or enamines. Chemically resistant, firmly adhering products with improved properties may be prepared by this process. The process described, however, is relatively complicated and therefore expensive. Further, the process is not universally applicable since only isocyanate prepolymers based on aliphatic polyisocyanates can be reacted with hydroxy ketimines with complete preservation of the ketimine structure.
According to German Offenlegungsschrift 2,338,256, high molecular weight, amine-terminated polyether urethane ureas are prepared by the reaction of prepolymers containing free isocyanate groups with amines in highly dilute solutions and then hardened with epoxide resins. The use of the solvents required for this process, in particular the aromatic solvents, is technically and physiologically undesirable. On the other hand, the viscosity of the solvent free reaction products is too high for practical use.
U.S. Pat. Nos. 4,291,146, 4,360,655 and 4,424,336 describe the use of relatively low molecular weight aminocrotonates as curing agents for epoxide resins. The use of the crotonates described in these references leads to cured epoxides which have poor flexibility for many purposes, i.e., less than about 30% elongation.
U.S. Pat. No. 5,021,537 describes a coating composition which comprises an epoxy resin, a polyacetoacetate, a curing agent for the epoxy resin and an optional solvent. Recently, novel amine compounds and processes for their production have been discovered. These compounds correspond to the formula: ##STR1## wherein A represents the polyfunctional radical left by the removal of the hydroxyl groups from a polyol of molecular weight of from 62 to 12,000, and preferably from about 800 to about 3500 and functionality n, R represents an arylene radical of from 6 to 21 carbon atoms, and n is an integer of from 2 to 6, preferably from 2 to 4. See U.S. application Ser. No. 523,769, filed on May 15, 1990. In addition, U.S. application Ser. Nos. 524,268, filed on May 15, 1990, and 562,293, filed on Aug. 3, 1990, relate to production techniques for similar compounds which can contain aliphatic as well as aromatic bound amine groups. Similar compounds and their methods of production can be found in U.S. Pat. Nos. 3,666,726 and 3,691,112 and in European Patent 363,000.
The present invention is directed to the discovery that the novel amine compounds noted are eminently suitable for use with epoxide group containing resins.